1. FIELD OF THE INVENTION
The present invention relates to an aqueous emulsion containing an aminoorganosiloxane modified by reaction with (a) a dialkyl pyrocarbonate, (b) dialkyl oxalate or (c) a mixture thereof, which emulsions impart reduced yellowing of textile fabrics and/or fibers when used as fabric softeners.
2. THE PRIOR ART
Fabrics have been treated for many years to improve their properties and acceptability to consumers. Improved softness (hand), reduction in static and greater ease in ironing are some of the desired properties. Some treatments used to achieve these results, however, are counter-productive. For example, application of durable press resins to improve ease of ironing is known to give fabrics a harsher hand. Also, some treatments to improve softness result in yellowing of the fabric.
It is well known to apply various types of textile conditioners to make textiles softer. By way of illustration, aminoorganosiloxanes and their aqueous emulsions have been widely used to impart superior softness and smoothness to natural and synthetic fibers and fabrics. However, in some applications, these aminoorganosiloxanes have a tendency to yellow fabrics and fibers. It is thought that the aminofunctionality is susceptible to oxidation and that this chemical reactivity may result in a variety of undesired chemical reactions which ultimately cause yellowing in some fabrics and fibers.
Some attempts have been made to modify aminoorganosiloxane. Several examples of modified aminoorganosiloxanes with reduced reactivity are known in the prior art. U.S. Pat. Nos. 2,929,829 and 2,928,858 disclose that organosiloxane containing acylamino groups can be prepared by the reaction of the corresponding aminosiloxane with carboxylic acids, esters, halides or anhydrides. Similar amide-modified organosiloxanes have been disclosed in U.S. Pat. No. 4,507,455.
Urea has been reacted with an organopolysiloxane having pendant diamine groups to provide organopolysiloxanes with ureido-substitution (U.S. Pat. Nos. 3,209,053; 3,702,860; and 3,772,351).
Japanese Kakai No. 59,179,854 (Chemical Abstracts, Vol 102, 63555 (1985)) relates to the reaction of polysiloxanes containing aminoalkyl groups with epoxy compounds, for example, glycidol. The products of this reaction are resistant to heat and oxidation and useful as softening agents for treating textiles.
Diethyl pyrocarbonate has been demonstrated to be a useful reagent to derivatize water soluble enzymes (Fedoresak I, Natarajan, A. T., Ehrenberg, L., Eur. J. Biochem., 10 450, 1969) and aminoacids (Burch, T. P., Ticku, M. K., Proc. Natl. Acad. Sci. U.S.A., 78 (6), 3945) in situ in aqueous solutions at ambient temperature. The reaction of diethyl oxalate with ammonia or an amine to produce an amide is known (Methods Der Organische Chemie, Houben-Weyl, Volume 8). However, there appears to be no prior art disclosing the use of such pyrocarbonates or oxalates with aminoorganosiloxane emulsions, particularly those for fabrics and fibers.